<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .box{
        /* width: 100%; */
        width: 300px;
        height: 300px;
        margin: 200px;
        box-sizing: border-box;

        border: 2px solid black;
        display: flex;
        flex-direction: row;
        background-color: #bfa;
    }
    .aaa{
        width: 50px;
        height: 100%;
        border: 1px solid red;
        box-sizing: border-box;
        /* flex: 0 0 auto; */
    }

</style>
<body>
    <div class="box">
        <div class="aaa">1111</div>
        <div class="aaa">2222</div>
        <div class="aaa">3333</div>
        <div class="aaa">4444</div>
        <div class="aaa">5555</div>
        <div class="aaa">6666</div>
        <div class="aaa">7777</div>
        <div class="aaa">8888</div>
        <div class="aaa">9999</div>
        <div class="aaa">1010</div>
    </div>
</body>
</html>